Mosquito season in DuPage County, IL: when it starts and ends
Mosquito months in DuPage County
In a normal year mosquito season in DuPage County, IL starts around April 18 and ends around October 22, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in DuPage County, and when
- Start tipping out standing water weekly by April 4.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 22.
- 99 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check IL spray notices.
DuPage County against the rest of IL
DuPage County has the 89th longest season of 102 IL counties, at 187 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 50.1°F.
- Cook County: April 20 to October 26 (189 days, 532 WNV)
- Bureau County: April 15 to October 20 (188 days, 0 WNV)
- Kendall County: April 18 to October 21 (186 days, 4 WNV)
- Kane County: April 19 to October 20 (184 days, 35 WNV)
West Nile in DuPage County
From 1999 to 2025, CDC ArboNET counted 355 human West Nile cases in DuPage County (224 neuroinvasive) across 23 years. The worst was 2012 with 56; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.